The product of the myc oncogene is responsible for the alteration of growth potential and induction of malignancy in cells in which the oncogene is active. The function of the myc protein has been studied by localizing the protein within the cell and examining the intracellular properties of the protein. Cells infected with the avian MC29 virus produce a hybrid protein, p110, which contains elements of both avian retrovirus and myc protein, and can be detected and quantitated by using antisera to either to these elements. Radiolabeled p110 migrates rapidly to the nucleus where it can be found in both chromatin-containing and nucleoplasmic fractions. The nucleoplasmic fraction contains about two-thirds of the initially labeled p110, which is degraded with a half-life of 30-40 minutes. The p110 in the chromatin- containing fraction has an extended half-life, about two hours. Steady-state analyses revealed a greater amount of p110 in the chromatin fraction than in the nucleoplasm, and the p110 associated with chromatin was found to be more highly phosphorylated than that in the nucleoplasm. Other studies indicate that p110 is associated with DNA, consistent with the in vitro binding properties of this protein. We suggest that the stability of the myc protein is dependent upon its association with DNA, and results with inhibitors of transcription suggest that the association of myc protein with chromatin is dependent upon transcription.